This invention relates to borescopes and endoscopes, which are long, flexible instruments which carry a viewing device at the end of an elongated insertion tube. Borescopes are intended for inspection of concealed machine parts and the like, for example, inspection of vanes of a turbine or jet engine without disassembly thereof.
The present invention is more particularly concerned with a detachable right angle reflector assembly that is demountably attached onto the viewing head on the distal end of the borescope insertion tube.
For many borescope applications forward viewing is required, but for other applications side viewing is needed. That is, it is sometimes necessary to view a hidden or obstructed target from a direction that is more or less radial with respect to the axis of the borescope. To permit both forward and side viewing with the same instrument, a detachable right angle optics assembly can be employed.
One detachable right angle prism assembly is shown and described in U.S. Pat. No. 4,727,859 to Raymond A. Lia. In that arrangement a housing is coupled by a bayonet fitting onto the viewing head, and includes a right angle prism that changes the viewing direction of the image sensor from axial (straight ahead) to radial (sideward). Because the assembly uses a bayonet coupling, alignment of the image sensor and the mirror or prisms is easily achieved, and the right angle viewer can be interchanged among several borescopes of the same type.
In many borescopes, particularly those which may have large, oversize illumination fiber bundles and/or wide viewing angles, the large outside diameter of the borescope distal tip presents a design constraint. In large-diameter borescopes, the use of a threaded coupling is required, rather than a bayonet mechanism. However, when the right angle viewer is attached by helical threads to the viewing head of the probe, each viewer and probe have to be made as a matched pair, and interchangeability is difficult or impossible to accomplish, since the alignment of the mirror or prism to the image sensor is determined by the amount of thread engagement. Matching thread engagements for a probe and a sideview mirror assembly are impractical to manufacture, because of variations in thread cutting and polish dimensions on the probe head.